Grade 12 – Chemistry in Everyday Life – Key Concepts in Chemistry

1. How do antacids work to relieve acidity in the stomach? Provide an elaborate explanation with reference to the principles of acid-base reactions and the functioning of antacids.

Answer: Antacids work by neutralizing excess stomach acid, which is primarily composed of hydrochloric acid (HCl). When antacids are ingested, they react with the HCl in the stomach to form water and a salt, thus reducing the acidity. This reaction can be represented as follows:

2HCl + CaCO3 -> CaCl2 + H2O + CO2

Here, calcium carbonate (CaCO3) is a common ingredient in antacids. It reacts with hydrochloric acid to produce calcium chloride (CaCl2), water (H2O), and carbon dioxide (CO2). The water and carbon dioxide are harmless byproducts that are easily eliminated from the body.

This neutralization reaction occurs because antacids are basic in nature and can accept the excess hydrogen ions (H+) from the stomach acid. By neutralizing the acid, antacids provide relief from symptoms such as heartburn and indigestion.

2. Explain the mechanism of action of antibiotics in treating bacterial infections. Provide a detailed explanation with reference to the principles of microbial growth and the mode of action of different classes of antibiotics.

Answer: Antibiotics are medications used to treat bacterial infections. They work by targeting specific aspects of bacterial growth and survival. The mechanism of action varies depending on the class of antibiotic.

One common mechanism is the inhibition of bacterial cell wall synthesis. Bacteria have a rigid cell wall composed of peptidoglycan, which provides structural support. Antibiotics like penicillin and cephalosporins target enzymes involved in the synthesis of peptidoglycan, thereby preventing the formation of a functional cell wall. This weakens the bacteria and makes them more susceptible to destruction by the immune system.

Another mechanism involves the inhibition of bacterial protein synthesis. Antibiotics such as tetracyclines and macrolides bind to specific components of bacterial ribosomes, which are responsible for protein synthesis. By interfering with this process, these antibiotics prevent the bacteria from producing essential proteins, leading to their death.

Some antibiotics disrupt bacterial DNA replication and transcription. For example, fluoroquinolones inhibit enzymes called topoisomerases, which are involved in DNA replication and repair. By targeting these enzymes, fluoroquinolones prevent the bacteria from replicating their DNA, thereby halting their growth and multiplication.

Overall, antibiotics exploit specific differences between bacterial and human cells to selectively target and kill bacteria. This specificity is crucial in minimizing harm to the human body while effectively treating bacterial infections.

3. Discuss the role of catalysts in chemical reactions. Provide an elaborate explanation with reference to the principles of reaction kinetics, activation energy, and the functioning of different types of catalysts.

Answer: Catalysts play a vital role in chemical reactions by increasing the rate of reaction without being consumed in the process. They achieve this by lowering the activation energy required for the reaction to occur. The activation energy represents the energy barrier that must be overcome for reactant molecules to transform into products.

Catalysts work by providing an alternative reaction pathway with a lower activation energy. They achieve this through various mechanisms, depending on the type of catalyst. Some common types of catalysts include enzymes, transition metals, and acid-base catalysts.

Enzymes are biological catalysts that facilitate biochemical reactions in living organisms. They possess a specific three-dimensional structure that enables them to bind to reactant molecules, forming an enzyme-substrate complex. This complex lowers the activation energy required for the reaction, allowing it to proceed more rapidly. Enzymes are highly specific and can catalyze specific reactions, making them essential for numerous biological processes.

Transition metals, such as platinum or palladium, are often used as heterogeneous catalysts in industrial processes. They provide a surface for reactant molecules to adsorb onto, facilitating their interaction and promoting the formation of products. Transition metals can also participate in redox reactions, transferring electrons between reactants and promoting the desired chemical transformation.

Acid-base catalysts function by donating or accepting protons during a reaction. They alter the acidity or basicity of the reaction environment, which can enhance the reaction rate. Acid-base catalysis is particularly important in organic chemistry, where many reactions involve the formation or breaking of covalent bonds.

In summary, catalysts accelerate chemical reactions by lowering the activation energy required for the reaction to occur. They achieve this through various mechanisms, including enzyme-substrate interactions, surface adsorption, and acid-base interactions. The use of catalysts is essential in many industrial processes and has significant implications for the efficiency and sustainability of chemical reactions.

4. Explain the concept of chirality and its significance in pharmaceutical chemistry. Provide a detailed explanation with reference to the principles of stereochemistry, enantiomers, and the biological activity of chiral compounds.

Answer: Chirality is a fundamental concept in chemistry that refers to the property of a molecule to exist in two non-superimposable mirror image forms, known as enantiomers. Chiral molecules possess an asymmetric carbon atom, also known as a stereocenter, which is bonded to four different substituents. The presence of chirality has profound implications in pharmaceutical chemistry.

Enantiomers have identical physical properties, such as boiling point and solubility, but exhibit different biological activities. This is because biological systems, such as enzymes and receptors, are often chiral and can differentiate between enantiomers. For example, the drug thalidomide was marketed in the 1950s as a sedative and anti-nausea medication. However, it was later discovered that one enantiomer caused severe birth defects, while the other enantiomer was therapeutically active. This tragic incident highlighted the importance of considering chirality in drug design and testing.

The biological activity of chiral compounds can be attributed to their interactions with chiral biomolecules. Enzymes, for instance, often possess chiral binding sites that can selectively recognize and interact with one enantiomer over the other. This can lead to differences in the pharmacokinetics, pharmacodynamics, and toxicity of chiral drugs.

To ensure the safety and efficacy of pharmaceuticals, regulatory agencies now require testing and characterization of drug enantiomers. This involves determining the absolute configuration of the drug molecule and assessing the biological activity of each enantiomer. The development of chiral separation techniques, such as chromatography and asymmetric synthesis methods, has enabled the production of enantiomerically pure drugs.

In conclusion, chirality plays a significant role in pharmaceutical chemistry due to the different biological activities exhibited by enantiomers. Understanding the stereochemistry of drugs is crucial for optimizing their therapeutic effects and minimizing potential side effects.